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Re: [PATCH v15 12/12] of: Add plumbing for restricted DMA pool

On 7/2/21 6:18 AM, Will Deacon wrote:
On Fri, Jul 02, 2021 at 12:39:41PM +0100, Robin Murphy wrote:
On 2021-07-02 04:08, Guenter Roeck wrote:
On Thu, Jun 24, 2021 at 11:55:26PM +0800, Claire Chang wrote:
If a device is not behind an IOMMU, we look up the device node and set
up the restricted DMA when the restricted-dma-pool is presented.

Signed-off-by: Claire Chang <tientzu@xxxxxxxxxxxx>
Tested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Tested-by: Will Deacon <will@xxxxxxxxxx>

With this patch in place, all sparc and sparc64 qemu emulations
fail to boot. Symptom is that the root file system is not found.
Reverting this patch fixes the problem. Bisect log is attached.

Ah, OF_ADDRESS depends on !SPARC, so of_dma_configure_id() is presumably
returning an unexpected -ENODEV from the of_dma_set_restricted_buffer()
stub. That should probably be returning 0 instead, since either way it's not
an error condition for it to simply do nothing.

Something like below?

Yes, that does the trick.



From 4d9dcb9210c1f37435b6088284e04b6b36ee8c4d Mon Sep 17 00:00:00 2001
From: Will Deacon <will@xxxxxxxxxx>
Date: Fri, 2 Jul 2021 14:13:28 +0100
Subject: [PATCH] of: Return success from of_dma_set_restricted_buffer() when

When CONFIG_OF_ADDRESS=n, of_dma_set_restricted_buffer() returns -ENODEV
and breaks the boot for sparc[64] machines. Return 0 instead, since the
function is essentially a glorified NOP in this configuration.

Cc: Claire Chang <tientzu@xxxxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Reported-by: Guenter Roeck <linux@xxxxxxxxxxxx>
Suggested-by: Robin Murphy <robin.murphy@xxxxxxx>
Link: https://lore.kernel.org/r/20210702030807.GA2685166@xxxxxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>

Tested-by: Guenter Roeck <linux@xxxxxxxxxxxx>

  drivers/of/of_private.h | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 8fde97565d11..34dd548c5eac 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -173,7 +173,8 @@ static inline int of_dma_get_range(struct device_node *np,
  static inline int of_dma_set_restricted_buffer(struct device *dev,
                                               struct device_node *np)
-       return -ENODEV;
+       /* Do nothing, successfully. */
+       return 0;



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